Heung-Jin Choi

Formation of a self-assembled phenylboronic acid monolayer and its application toward developing a surface plasmon resonance-based monosaccharide sensor

For the surface-optoelectronic study of sugar sensing, we synthesized and characterized dithiobis(4-butyrylamino-m-phenylboronic acid) (DTBA-PBA) as a recognition molecule. DTBA-PBA has a boronic acid group that has been known to form covalently bonded complexes with the 1,2- or 1,3-diol of sugars. A self-assembled monolayer (SAM) of DTBA-PBA was formed on a gold surface and characterized by atomic-force microscopy, Fourier transform infrared reflection absorption spectroscopy, and surface electrochemical measurements. An interaction study between monosaccharides and DTBA-PBA SAM was performed using surface plasmon resonance spectroscopy. The increase in molecular interactions between DTBA-PBA SAM and monosaccharides resulted in an optically induced electron excitation change on the Au surface through a refractive index change of the interfacial recognition layer. This correlation between electron excitation and molecular interaction was measurable at very low monosaccharide concentrations (1.0 x 10(-12)M). DTBA-PBA SAM shows a selective fructose sensing among four kinds of monosaccharides, even in a low concentration range.

Ruthenium-catalyzed regioselective synthesis of 2-substituted indoles via ring-opening of epoxides by anilines

Anilines react with epoxides in dioxane at 180°C in the presence of a catalytic amount of a ruthenium catalyst along with tin(II) chloride to afford 2-substituted indoles in moderate to good yields.

Isolation and characterization of the major colorant in Gardenia fruit

Abstract The major yellow colorant from the fruit of Gardenia jasminoides was isolated and then identified with the aid of FAB–MS, UV/visible and NMR data. The NMR assignments were based on data from 1H NMR, 13C NMR, DQF–COSY, NOESY, HMQC and HMBC measurements. Molar absorptivity was determined using an analytically pure sample of crocin.

Synthesis of isoindolin-1-ones via palladium-catalyzed intermolecular coupling and heteroannulation between 2-iodobenzoyl chloride and imines

Abstract 2-Iodobenzoyl chloride reacts with an array of imines in acetonitrile–methanol under carbon monoxide pressure in the presence of a catalytic amount of bis(triphenylphosphine)palladium(II) chloride/triphenylphosphine together with triethylamine to afford the corresponding isoindolin-1-ones in moderate yields.

Enhancement of BSA Binding on Au Surfaces by calix(4)bisazacrown Monolayer

Effective investigation of biomolecular structure and function with chip-based modern instruments often requires reliable and steady attachment of designated biomolecules on substrate. Here, we investigated the formation of self-assembled monolayer (SAM) with a new calix[4]arene derivative containing bisazacrown ether at the lower rim (calix[4]bisazacrown) where ammonium moieties of proteins can mainly be interacted with. Immobilization process of protein using bovine serum albumin (BSA) on the Au surface modified with calix[4]bisazacrown monolyer as an artificial linker system was monitored by surface plasmon resonance (SPR) technique. The surface concentration of BSA calculated by the simulation of SPR experimental data was higher than that of a well-known similar commercial protein linker. These results can help in modeling and understanding of protein immobilization on solid surface as well as further development lab-on-a-chip (LOC) devices for biomedical diagnosis kit of certain protein related diseases as biomarkers.

Building a novel vitronectin assay by immobilization of integrin on calixarene monolayer

Membrane proteins possess significant hydrophobic domains and are likely to deplete their native activity immobilized on the solid surface relative to those occurring in a membrane environment. To investigate an efficient immobilization method, calix[4]crown-ether monolayer as an artificial protein linker system was constructed on the gold surface and characterized by Fourier transform infrared reflection absorption spectroscopy (FTIR-RAS), atomic force microscopy (AFM) and cyclic voltammetry (CV). Integrin alpha(v)beta3 was functionally immobilized onto the monolayer and the integrin-vitronectin interaction was investigated by surface plasmon resonance (SPR). It was found that calix[4]crown-ether was assembled as a monolayer on the gold surface. Orientation and accessibility of integrin alpha(v)beta3 was assessed by sensitive binding of its natural ligand, vitronectin at pg mL(-1) level. Moreover, surface coverage of integrin layer and thickness calculated through SPR curve simulation verified that integrin layer was a monolayer in activated form. In combination with the SPR method, this calix[4]crown monolayer provided a reliable and simple experimental platform for the investigation of isolated membrane proteins under experimental conditions resembling those of their native properties.

An aqueous friendly chemosensor derived from vitamin B6 cofactor for colorimetric sensing of Cu2 + and fluorescent turn-off sensing of Fe3 +

Chemosensor L derived from vitamin B6 cofactor pyridoxal-5-phosphate was investigated for the selective detection of Cu(2+) and Fe(3+) in aqueous medium. Sensor L formed a 1:1 complex with Cu(2+) and displays a perceptible color change from colorless to yellow brown with the appearance of a new charge transfer band at ~450 nm. In contrast, the fluorescence of L was quenched selectively in the presence of Fe(3+) without any interference from other metal ions including Cu(2+).

PALLADIUM-CATALYSED CONVENIENT SYNTHESIS OF 3-METHYLENEISOINDOLIN-1-ONES

ABSTRACT 2′-Bromoacetophenone reacts with an array of aliphatic primary amines under carbon monoxide pressure in the presence of a catalytic amount of a palladium catalyst to afford 3-methyleneisoindolin-1-ones in moderate yields.

Preparation and properties of soluble aromatic polyetherimides based on 2,2‐bis[4‐(3,4‐dicarboxyphenoxy)phenyl]hexafluoropropane dianhydride

Aromatic polyetherimides were synthesized from a fluorine containing aromatic carboxylic acid dianhydride, 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]hexafluoropropane dianhydride (6F-BABPA) and five typical aromatic diamines including 1,1-bis(4-aminophenyl)-1-phenyl-2,2,2-trifluoroethane (3F-DAM) by two-step procedures—amidation to polyamic acids (PAA), followed by thermal imidization of PAA. The chemical and physical properties of the newly prepared polyetherimides (PEI) were compared in terms of their chemical structures, inherent viscosities, mechanical, and thermal properties. All polyetherimides were well soluble in common organic solvents such as N-methyl-2-pyrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), pyridine, and methylene chloride. A PEI prepared from 6F-BABPA/3F-DAM was especially easily dissolved in NMP. The glass transition temperature (Tg) range of the obtained PEI was 209–257°C. The dielectric constants and refractive index were 2.8–3.2 and 1.61–1.56, respectively. The polyetherimide, 6F-BABPA/BAPP, with a low fluorine content (11.4% fluorine content), has 0.99% water absorption, whereas the polyetherimide, 6F-BABPA/4-BDAP, having a high fluorine content (26.0% fluorine content) showed 0.35% of water absorption.

Remarkable Change in Fluorescence Emission of Poly(diphenylacetylene) Film via in situ Desilylation Reaction: Correlation with Variations in Microporous Structure, Chain Conformation, and Lamellar Layer Distance

Fluorescence (FL) emission properties, microporous structures, energy-minimized chain conformations, and lamellar layer structures of the silicon-containing poly(diphenylacetylene) derivative of p-PTMSDPA before and after desilylation were investigated. The nitrogen-adsorption isotherms of p-PTMSDPA film before and after desilylation were typical of type I, indicating microporous structures. The BET surface area and pore volume of the p-PTMSDPA film were significantly reduced after the desilylation reaction, simultaneously, its FL emission intensity remarkably decreased. The theoretical calculation on both model compounds of p-PTMSDPA and its desilylated polymer, PDPA, showed a remarkable difference in chain conformation: The side phenyl rings of p-PTMSDPA are discontinuously arranged in a zig-zag pattern, while the PDPA is continuously coiled in a helical manner. The lamellar layer distance (LLD) in the p-PTMSDPA film significantly decreased after the desilylation reaction.